Catalyst compositions based on well defined donor ligand containing metal complexes, referred to as post-metallocene complexes have been shown to give products having better comonomer incorporation and narrow molecular weight distribution. However, these catalysts often have poor high temperature stability and suffer from poor catalytic efficiencies, especially at elevated polymerization temperatures. When employed to prepare ethylene, α-olefin and diene containing polymers, especially ethylene, propylene, and ethyl idenenorbornene (ENB) containing polymers, the resulting polymer molecular weight and comonomer incorporation ratio is often deficient.
Examples of one type of the foregoing post metallocene catalysts are disclosed in U.S. Pat. No. 6,897,276, where Group 3-6 or Lanthanide metal complexes, preferably Group 4 metal complexes, of bridged divalent aromatic ligands containing a divalent Lewis base chelating group are disclosed.
Higher solution reaction temperatures are particularly desired for ethylene/α-olefin/diene polymerizations in order to improve operating efficiency. However, the use of higher reaction temperatures often results in poor α-olefin and diene conversions. Accordingly, selection of catalyst compositions capable of incorporating increased amounts of α-olefin and diene comonomers at elevated reaction temperatures is highly desired.
We have now discovered that certain metal complexes may be employed in a solution polymerization process to prepare high molecular weight ethylene containing interpolymers containing relatively large α-olefin and diene contents. The resulting polymer products possess desirable properties such as increased tensile properties, reduced density (greater comonomer incorporation) and improved high temperature performance. In addition, we have discovered that these catalyst compositions retain their high catalyst activity using relatively low molar ratios of conventional alumoxane cocatalysts. The use of reduced quantities of alumoxane cocatalysts (reduced by up to 90 percent or more, compared to the quantities employed in conventional processes) allows for the preparation of polymer products having reduced metal content and consequently increased clarity, improved dielectric properties and other enhanced physical properties. In addition, the use of reduced quantities of alumoxane cocatalysts results in reduction in polymer production costs.